1. Field of the Invention
The present invention is related to a method for transmitting messages in an elevator group control system.
2. Description of the Prior Art
In an elevator communication system, all communication data originating from a separate group controller is not transmitted to a plurality of elevator controllers at almost the same time. If all communication data were transmitted from the group controller to the elevator controllers within a predetermined period, this large communication burden could cause a jam in the processing of the communication data. Accordingly, transmission efficiency is regarded as a major factor in the quality of such a control apparatus.
FIG. 1 is a simplified block diagram of a conventional elevator communication system.
Referring to FIG. 1, the elevator communication system consists of a plurality of elevator controllers 12A-12K, each associated with a floor of a building, to execute elevator-related signaling and control the execution of necessary operations; group controller 11 to execute group-related signaling and dispatch functions; and a common network NET to associate the elevator controllers 12A-12K and the group controller 11.
FIG. 2 is a block diagram illustrating a communication control circuit in the conventional elevator communication system.
As illustrated in FIG. 2, employed in the group controller 11 illustrated in FIG. 1 are a plurality of group communication controllers 21A-21K. A plurality of elevator communication controllers 22A-22K are employed in elevator controllers 12A-12K, respectively, and communicate with the group communication controllers 21A-21K via exclusive communication lines in a one-to-one parallel fashion.
The operation of the elevator communication system described as above, will be explained with reference to FIGS. 3 through 6.
If a passenger who is standing on the 8.sup.th floor selects a hall call such as "down" via a control panel (not shown) associated with one of the elevator controllers 12A-12K the corresponding elevator communication controller 22A-22K recognizes an inputting-signal of hall call and transmits the data to the corresponding group communication controller 21A-21K.
Next, after a predetermined time, the group communication controller 21A-21K retransmits the transmitted data to the corresponding elevator communication controller 22A-22K to execute the operation as ordered. This confirms the correctness of the transmitted data.
In the retransmission operation, the communication data, which is data transmitted from the group communication controller 21A-21K to elevator communication controller 22A-22K or vice versa, consists of 1) data number and 2) associated data. FIG. 3 illustrates a table of communication data stored at the group controller 11 by each group communication controller 21A-21K for a respective elevator communication controller 22A-22K. The data number represents an index indicating a data record for the data transmission, while the region labeled data is where the actual data is stored. For example, in case that a data number "3" is assigned to the transmission data of calling the elevator car from the 1.sup.st to the 8.sup.th floor, the elevator communication controller 22A-22K executes a recording operation and records "3" as the data number in FIG. 3 and "the hall call from 1 to 8 floor" in the data region in FIG. 3. Subsequently, the group communication controllers 21A-21K for the first floor outputs the communication data as retransmission data to the corresponding elevator communication controller 22A-22K.
FIG. 4 illustrates a transmission data storage table stored at each group communication controller 21A-21K with respect to the associated elevator communication controller 22A-22K in the conventional communication system. This table is used to transmit changed data after comparing present data with previous data stored in the group communication controller 21A-21K.
FIG. 5 is a flow chart showing how transmission data, data for transmission to one of the elevator communication controllers 22A-22K from one of the group communication controllers 21A-21K, is created by one of the group communication controllers 21A-21K.
Referring to FIG. 5, the retransmission data is determined in step S1 by one of the group communication controllers 21A-21K, and the data number is initialized by "1" in step S2 (the number "1" is an index indicating a record of the transmission data storage table as illustrated in FIG. 4). For instance, if the data number is "2", a comparative data is "data 2" of the table illustrated in FIG. 4.
Next, a test S3 is performed to determine if any changed data is created with respect to all communication data; namely, determine whether the table of FIG. 3 includes new data. If the test S3 is affirmative, the overall program is returned to a transfer point T1. But if test S3 is negative, a test S4 is executed to determine if the communication data fills the communication data table of FIG. 3. That is to say, if a communication buffer in the group communication controller 21A, 22B, . . . or 21K for the record is not fully filled, the program is returned through a transfer point T2.
But if the test S4 is negative, a test S5 is executed to check if the present data is identical to the data recorded in the transmission table. If not, the relative data number and the actual data are recorded on the record region in the transmission table of FIG. 4 which will be transmitted in step S6. Subsequently, the data number is increased by "1" to process the next data in step S7. But if the test S5 is negative, the step S7 will also be executed.
FIG. 6 is a flow chart showing how the retransmission data is created in the conventional control apparatus.
The flow chart illustrated in FIG. 6 is a subroutine for determining the retransmission data in step S1 of FIG. 5. In FIG. 6, a test ST1 determines if the retransmission data number stored in the group controller 11 is a maximum data number, i.e., if the number is bigger than the largest possible data number for the transmission data storage table of FIG. 4. If the test is affirmative, the retransmission data number is initialized to 1 in step ST2. However, if the test is negative, the data of the transmission data storage table indicated by the retransmission data number is recorded on the data record to be transmitted in step ST3. Subsequently, the data number is increased by "1" in the next data step ST4.
According to the conventional process for creating the retransmission data as described above, it is noted that if the maximum data number recorded on the transmission table is 48 and the transmission period for the data record to be transmitted is 32 ms, the maximum time it takes to retransmit the data record, wherein the data record has already been transmitted, is 1,536 ms (T=48.times.32 ms).
The number of the data which each of the group communication controllers 21A-21K transmits to the corresponding elevator communication controller 22A-22K is predetermined as 8. So, when the number of the data to be transmitted is 4, another 4 data should be added thereto for transmission.
For that reason, there are drawbacks that the transmission time is delayed, thereby putting a large burden on communication processing.
Further, in case that the elevator cars connected to the group controller 11 are 5 and the communication period is 32 ms, the time it takes to transmit the record for 5 elevator cars is 160 ms (T-5.times.32 ms), since the group controller 11 has been communicated with each elevator car via the common network NET.
Accordingly, in the conventional elevator communication system, when the records are transmitted, an unnecessary region, where no information is recorded, is also transmitted together because the record length is already predetermined. In the example above, another four records were added to reach the predetermined number of records (i.e., eight), even though only four records needed to be sent. Further, if several elevator cars need to transmit the records at almost the same time, there is a drawback of a heavy burden in the communication process since each elevator car does not recognize the present operations of each elevator controller.